Silicon materials such as silicon (Si) and silicon oxides represented by SiOx are known to store more lithium ions per unit volume than carbon materials such as graphite. In particular, SiOx has been studied for use in negative electrodes in lithium ion batteries and the like because its volume change by the intercalation of lithium ions is smaller than that of Si. However, SiOx has low conductivity as compared to graphite. Negative electrode materials have been then presented in which the surface of SiOx particles is coated with carbon to enhance the conductivity (see, for example, Patent Literature 1). Further, to attain enhanced cycle characteristics, Patent Literature 2 discloses a negative electrode material obtained by mixing graphite with carbon-coated SiOx particles.